1. Field of the Invention
The present invention relates generally to a grinding machine and, more particularly, to an apparatus for successively truing and dressing a grinding wheel made of hard abrasive, such as cubic boron nitride.
2. Description of the Prior Art
In truing a so-called CBN grinding wheel made of cubic boron nitride, heretofore, it has been attempted to use a truing device with a silicon carbide grinding wheel. In such a prior art truing technique, the device is first placed on a worktable of a grinding machine, and relative feed movement is then made between the CBN wheel and the worktable, whereby the truing of the CBN wheel is carried out. The CBN wheel is further required to be dressed after truing. In a prior art dressing technique therefor, an abrasive impregnated wax stick is employed and applied to either the wheel surface of the CBN wheel or the cylindrical surface of a workpiece. When contact is effected between the CBN wheel and the workpiece, the liberation abrasive grain intervening therebetween serves to grind and remove bond material from the wheel surface so as to thereby open a plurality of pores thereon.
The prior art truing and dressing techniques, however, depend on the manual labor of an operator, and therefore raise many problems not only with respect to the safeness of the work, but also relating to the accuracy and efficiency of the truing and dressing operations. Most especially, as human intervention is required, both techniques are impossible to be applied to grinding machines which are fully automatized for use in a mass-production line.
With the dressing technique, moreover, wear of the CBN wheel is undesirably increased. More specifically, since the size of the pores opened on the wheel surface largely influences the metal removing ability of the CBN wheel, as generally known, abrasive grain used in dressing has to, therefore, be determined in taking consideration of the metal removing ability which is asked of the CBN wheel. If it is tried in the prior art technique, nevertheless, to open large pores on the wheel surface by the use of grain of significant size, excessive removal of the wheel bond material is necessarily brought about, due to the fact that complete contact is made between the workpiece and the CBN wheel, thus facilitating CBN abrasive grain to fall from the wheel surface. In addition, since the stick employed in dressing has as its chief ingredient a wax, such as polyethylene glycol, using the stick allows the grain for dressing to be scattered and deposited on the machine, and, in consequence, frequent maintenance for the machine becomes necessary.